Conventionally, a variety of techniques for providing a voice which does not include noise and which is easy for the user to hear are disclosed. For example, patent reference 1 discloses a technique of using a noise removal parameter which is stored in a noise removing unit and which is set up immediately before weighting is stopped to extract only a voice signal from a signal in which a voice and steady noise are mixed and carry out digital encoding on the voice signal. Further, patent reference 2 discloses a technique which is constructed in such a way as to, when it is hard to catch a voice or a sound outputted from a speaker, allow the user to operate an adjusting unit to change the characteristics of the voice or sound, thereby making it easy for the user to discriminate between a voice and noise or the like. In addition, patent reference 3 discloses a technique of determining an energy value calculated on the basis of a sound source parameter at the time of sound reproduction, selecting a predetermined gain according to the energy value determined, and correcting the volume of the reproduced sound of the voice data according to the selected gain.